Calcareous
Nannofossils

What are Calcareous Nannofossils?

Calcareous
nannofossils are fossil remains of golden-brown, single-celled
algae that
live only in the oceans. Because they are plants they need sunlight, so they
float near the surface of the water. There are billions and billions of them
living in the oceans today, and they are eaten by anything that is bigger than
they are. They are one of the primary organisms at the base of the food chain.

These algae make tiny
calcite
platelets inside their cells, and these platelets (the calcareous nannofossils
or nannos for short) move to the surface of the cell. No one is certain why
these platelets are formed, but after a while they fall off the cell and slowly
drift down to the bottom of the ocean. These platelets are replaced by new ones
that constantly are forming within each cell. As these platelets land on the
bottom of the ocean, they are slowly covered up with remains of other plants
and animals and bits of mud and sand that have washed out with the rivers of
the world. At this point they are part of a mud or marl or sandy clay.
Eventually, there are many sediments on the ocean bottom, and their weight is
enough so that the lowest sediments are squeezed enough to become rocks. If
these rocks are almost entirely made of nannos, they are a chalk. If there
aren't so many nannos, they can be part of a limestone or shale. These calcite
platelets are preserved in the rocks and are the fossils that paleontologists
study.

Calcareous nannofossils have been living in the world's oceans for at least
200 million years (from the
Triassic Period),
and they have evolved and changed constantly over time. For example, if a
paleontologist looks at an ocean bottom sediment from 1 million years ago and
compares it to a sediment that was deposited 60 million years ago, most of the
nannos in the two samples will be completely different species. A calcareous
nannofossil specialist can look at ocean bottom sediment from anywhere in the
world that was deposited less than 200 million years ago (one which does
contain calcareous nannofossils) and be able to tell you how old that sediment
is. And he/she would be accurate within 1-4 million years or even less.

Application to Earth Science Research

Biostratigraphy - Calcareous nannofossils are the most
useful age indicator for marine sediments from the
Jurassic to
the Recent because of their rapid rate of evolution and wide geographic
distribution. The first appearance datums (FAD's) and last appearance datums
(LAD's) for calcareous nannofossil species usually occur at the same horizon
globally and often can date sediments to accuracies of one million years or
less. Accurate dating of sedimentary deposits has many practical applications.
For example, calcareous nannofossils have been used successfully to help map
both the surface and subsurface geographic extent of lithologic units,
particularly in regions with complex facies patterns like New Jersey and
Alabama. They also are used in regional geologic studies to correlate time-
equivalent but lithologically distinct deposits from state to state and region
to region.

Paleoceanography, Paleobiogeography, and Paleoecology -
Calcareous nannofossils can be used to help determine the temperature and
current patterns of ancient oceans. For example, if a species lived only in
warm tropical waters, then its presence can be used to trace the geographic
extent of tropical waters through time. Thus, species B, which has been found
in Campanian
sediments only off the coast of present-day Florida, ranged from Florida to New
Jersey during the
Maastrichtian.
From this we can conclude that in the region north of Florida, ocean
temperatures were warmer during the Maastrichtian than during the Campanian.
Similar paleobiogeographic fossil data are useful in determining ancient
climates, species migration patterns, and continental relationships.

Forensic, Art, and History Studies - Calcareous
nannofossils have been used to help police solve criminal cases. For example,
clay scraped from the shoes of a murder suspect in England contained calcareous
nannofossil species that were unique enough to lead the police to the scene of
the crime. Calcareous nannofossils have been used to determine the origin of
building stones for Medieval churches in Denmark and to check authenticity of
paintings. In Norway, which has no native chalk, calcareous nannofossils were
used to determine the origin of white chalk that was used to prepare the
surfaces of Medieval wooden sculptures and panels before painting. The pattern
and changes through time of the chalk trading routes probably can be used to
interpret general trading patterns in northern Europe at the same time.

Current USGS Projects using Calcareous Nannofossils

Southeastern Coastal Plain Project - Both
Mesozoic and
Cenozoic
calcareous nannofossils are an important part of the South Carolina Coastal
Plain Study that is within this project. During the projected five-year extent
of this project, calcareous nannofossils will be used as the primary tool to
determine the age of marine sediments that are found both at surface outcrops
and in numerous coreholes in South Carolina and eastern Georgia. In addition to
using previously collected sediments, this project is actively gathering new
material by means of (1) coreholes, (2) auger holes, and (3) outcrop sediments.
The calcareous nannofossil data, in conjunction with other fossil data and
lithologic and geophysical data, will be used to establish a stratigraphic
framework for the study area. This framework will form the basis for a widely
applicable, comprehensive digital database that encompasses the principal
geologic and geohydrologic characteristics of the surface and subsurface
Cretaceous and
Tertiary strata in
South Carolina. Other fossil groups used in this project:
Dinoflagellates,
Ostracodes, and Pollen.